As the economy dips and gas prices rise, more people choose to enhance the insulation in their existing homes rather than purchasing new homes. Government credits and utility company discounts give homeowners an opportunity to afford adding more insulation. Not all insulating techniques result in the same performance. This article addresses two different techniques related to insulating existing exterior walls.
Blown Fiber Materials are Designed to be Packed
Cellulose, fiberglass and far less common, rockwool are all designed to be packed. When insulating material is not packed, it loses insulating performance. A recent study contrasted the difference between a wall that was gravity “packed” and one that was dense packed to 3.5 psi. The results are not surprising. The dense pack wall outperforms the gravity “packed” wall. Why? Note the difference in insulating an existing wall.
The word “packing” has quotes because this technique does not really involve packing. A hole is drilled into the uppermost part of the wall cavity. The insulator blows the material into the cavity, allowing the material to naturally fall into the cavity. The material fills the cavity, but there is no measurable packing density.
Unfortunately, this technique is quite popular. Even respected home remodeling shows demonstrate this technique. Will it improve an existing house’s insulating performance? Sure. But the insulating performance is inferior to the technique below. Also, the insulation will settle creating gaps. If the home has a brick exterior, gravity packing is nearly the only option. That is, unless the homeowner lets you drill holes inside their homes.
Problems with this technique:
- These cavities are inconsistently packed. There is no measurement of the density of the material falling into the cavity, so there is no way an insulator can control the flow of material. There is a lot of guess work. The wall cavity, at the hole will be packed with greater density than the rest of the cavity.
- These cavities often have voids. When the falling material hits a wire or plumbing that intersects the cavity, the material sometimes clumps on top of the obstruction and prevents a complete filling of the cavity.
- Fiber materials are prone to settling—cellulose especially. When installing loose fiber into a cavity, the air is increased to prevent hose blockages. After installation, the material will eventually settle, leaving a void at the top of the cavity.
The best insulating standards involve packing fiber material with a minimum of 3.5 psi. Typically, a hole is drilled at the bottom of the wall cavity [1. Some will drill a hole at the top, but it is really of no consequence]. The insulation hose is reduced down to 2,” 1.5″ or even 1.25.” A clear vinyl tube is inserted into the hole. This hose is 10 feet long and allows the insulator to insert it into the cavity all the way to the top sill plate which guarantees that the insulation will not get hung up on obstacles. As the insulation packs into the cavity, the operator can see the material flow stop in the tube and will pull it out as it continues to pack the cavity.
The Cool Machine brand, has a gauge on the airlock which will give the installer a definitive PSI setting.
Advantages of this technique:
- The insulation is installed with a consistent density. The material at the top, middle and bottom of the cavity will have the same density.
- There is no guess work. The insulator will confidently be able to fill the cavity, knowing that there are no voids.
- The fiber materials, having been packed into the cavity, will not settle.
- The insulation performs to its full potential.